Phase-sequence relaying



p 1942. E. L. HARDER 2,296,784

PHASE-SEQUENCE RELAYING Filed May 31, 1940 WITNESSES: I INVENTOR W E020? L. #070 67:

. 94 ZMFMM BY ATTORNEY Patented Sept. 22, 1942 PHASE-SEQUENCE RELAYINGEdwin L. Harder, Forest Hills, Pa., assignor to Westinghouse Electric &Manufacturing Company, East Pittsburgh, Pa.-, a corporation ofPennsylvania Application May 31, 1940, Serial No. 338,093

14 Claims.

My invention relates to relays for the protection of transmission linesand other electrical devices in the event of the occurrence ofovercurrent or a fault.

In my Patent No. 2,183,646, issued December 19, 1939, and assigned tothe Westinghouse Electric & Manufacturing Company, a system is shownwhereby a single discriminating function may be obtained by the vectoraddition of quantities derived from the positiveand zero-sequencecurrent-components of the line-currents, the negative-sequencecurrent-component being excluded, which quantities are suitably weightedso that the distriminating function will be maintained withincontrollable and adjustable limits for the different kinds of faults.The weighting is so chosen that the limits of the discriminatingfunction are kept within a relatively narrow range so that asingle-element relay will register, no matter which of the ten differenttypes of faults might occur.

In the instant invention I disclose another relaying apparatus which,however, utilizes the scalar addition of quantities, derived from thesequence-components of the line-currents, for obtaining the singlediscriminating function. The quantities may also be suitably weighted,depending primarily on how well the protected line is grounded, so thatthe discriminating function will also be within a narrow range for thedifferent types of expectable faults.

In one specific embodiment of the instant invention the weighting issuch as to build up the discriminating function due to line-to-linefaults,

to a value close to the discriminating function expectable from athree-phase fault.

In accordance with my invention I do this by introducing an electricalquantity which is representative of the negative-sequence component ofthe line-currents. However, the introduction of this component does notdecrease the sensitivity of the apparatus, that is, the value of thediscriminating function, to double line-to-ground faults.

It is an object of my invention to provide a protective means in whichthe quantities representative of the different sequence-components ofthe line-currents are numerically combined for controlling asingle-element relay by a responsive registration, or discriminatingfunction, whose sensitivity to the different types of expectable faultson the line can be controlled by selecting the sequence-components to becombined, suitably weighted if necessary, and converted to scalarquantities before their combination. The

resulting discriminating function is unidirectional so that the relativephase angle relationships of the phase-sequence quantities, which arevectorial, are of small consequence in the registered response.

By suitably selecting which of the scalar quantities, derived from thedifferent phase sequencecomponents, are to be combined, a discriminatingfunction obtains which will be close to a predetermined magnitude asfaults rotate from phase to phase, which will be within a small range ofthis magnitude whatever the phase relationships of the phasesequence-components,

and which will vary only slightly between the different possible typesof faults; that is to say, if the level of the discriminating functionobtained from a three-phase fault is the base value for comparison, thelevel of the discriminating function obtained from any combination oflineto-line faults, and any combination of line-toground faults,especially double line-to-ground faults, can readily be made toapproximate the base value.

My invention has many of the advantages described in my aforesaidpatent, and it is also particularly useful for protective purposeswithin a station where pilot wires are not involved, or for overcurrentprotection, or for pilot wire protective systems where the magnitude ofcurrent-flow to or from one end of the protected section having aninternal fault will be different from that of the current-flow to orfrom the other end, as for example, in a radial distribution system, ora loop distribution system where the protected section has one terminalclose to an energy supply but the other end relatively far from theenergy supply.

Where my invention is utilized in pilot wire systems, the unidirectionalcharacter of the discriminating function prevents the use of insulatingtransformers but the terminal equipment can be adequately protectedagainst extraneously induced voltages in the pilot wires by means ofselfexcited neutralizing transformers, such as described and claimed inmy copending application, Serial No. 212,451, filed June 8, 1938, andassigned to the Westinghouse Electric 8: Manufacturing Company.

Additional objects and features of my invention will become apparentfrom the following description thereof, taken in conjunction with theaccompanying drawing in which like numerals generally indicate likeparts, and in which:

Figure 1 is a diagrammatic view of circuits illustrating a network forobtaining scalar quantities representative, respectively, of the zero-,positiveand negative-sequence-components of the line-currents in anelectric device, shown in this figure as a three-phase line;

Fig. 2 is a diagrammatic view of circuits and apparatus embodying myinvention, for a protective system for a section of a three-phase linewherein the protective system includes pilot wires. This viewillustrates a modified form of my invention in which the discriminatingfuncconductor 22 of the tion is obtained by the scalar combination ofquantities due to zeroand positive-sequence current-components; and,

Fig. 3 is a diagrammatic view of a further modification, andparticularly showing my inven-;

tion applied to overcurrent protection. 7 I,

My invention comprises, generally, the scalar combination of quantitiesderived from selected phase-sequence current-components of thelinecurrents in an electric device, and-infFig. 1 I show how adiscriminating function may be obtained which may be represented by theequation in which all quantities between vertical bars are absolute orscalar values. In Equation 1 the subscripts 0, l and '2 are respectivelyindicative of zero-sequence, positive-sequence, and negativesequencecomponents 'of the three-phase linecurrent's flowing in lines a, b'a'ndc, the respective currents in which maybe represented 'by I with asubscript corresponding to the particular line involved. The generalsymbols employed in this descriptio nfo'llow those described 'in thebook Symm etrica1 Components by 'CJFJWagner and R. D. Evans.

The "filter network, in which the sequencecomponents are obtained, isenergized from the three phase line, a,'b, 0, through a single set ofcurrent transformers 2, '4 'and 6, which are" "obtained from one filtersection "P; an electrical quantity representative of the rotational"negative-sequence component may be obtained from another filter sectionN; and an electrical quantity representative of the zero-sequencecomponent may be obtained from still another filter section Zn.

The section P is very similar to thepositive sequence network sectiondescribed in Fig. 1 of my aforesaid patent, and comprises anlimpedance 2having a secondary winding M inductively coupled to two primary windings1'6 and 18 in two circuits traversed, respectively, by'the currents Iband Ic. This-section further includes a resistor 20, having avalue3R,'which is traversed at least in part by the line-current Ia flowingto a neutral conductor 22. The neutral conductor 22'is connected to thepoint of the resistance 20 so that the discriminating factor across theterminals 24 and 26 is due solely to the vpositive-sequence component ofthe line currents Ia, Ib and I0. To obtain this the mutual reactancesbetween the windings l4 and I6, and the windings l4 and I8 are madeequal to a /3R, and by tapping off the neutral cope point of theresistance =20, the discriminating factorlcili across the terminals '24and 26 will be due solely to the positive sequence current I1, asmore-fully'explained in my aforesaid patent, with the weighing-factor7c, in that patent. for

A resistance 34 of a value has one end connected to an end of thewinding'28, and its other end to a terminal 35 which is paired with aterminal 38 connected to the other end of the winding 28. Connectedacross the resistance (fl! is a secondary winding 48 of a transformer Xhaving a primary winding 42 traversed by the c'urrent I-a and 'a primarywinding traversed by the current -Ib+Ic. The winding 42 has twice thenumber of turns'of the winding 44 which in the preferred form equals thenumber o'f turns in the secondary winding 40.

The impedance Y, the transformer X, and the resistance 34 composethe'sec'tion N of the network, and will produce a discriminating factoracross the terminals '36 and 33, which isre- 'sponsive only to thenegative=sequence component of the'line-currents.

A mathematical explanation of this section is as follows: With nocurrent flowing through the terminals 36 and 38, a, circuit may betraced in which the sum of all the voltage dropsthrough the circuit,including connection Mi, the primary winding 23, the resistance "34, andconnection 48, must equal the voltage Em across'th'e terminals 36 and38, as follows:

R1, R Ib+ 16 a elbwa line-currents Ia, Ib and In, which are representedby and remembering that By reducing Equation 3, it will be found thatall the In terms, and all the I1 terms add up to zero, and thatindicating that the discriminating factor across the terminals 36 and 38is due solely to the negative-sequence component of the line-currents.

The neutral conductor 22 connects to one end of a resistor R0, the otherend of which is connected to a further neutral conductor 50 connected tothe neutral point of the Y-connected current transformers. Consequently,as is well known in the art, the drop across this resistance R0 will bedue solely to the zero-sequence component flowing in the neutral lines22 and 50. Terminals 52 and 54 are connected across this resistor R0 sothat an electric voltage-quantity R0I0=K0Io is manifest across theseterminals, which will be representative solely of the zerosequencecomponent In of the line-currents.

The different discriminating factors across the respective pairs ofterminals 2426, 3638, and 52-54, are, in this particular instance,converted to scalar quantities by connecting full-wave rectifiers 56,58, and 60, respectively, across the pairs of terminals. The directcurrent outputs of the rectifiers are algebraically added by beingconnected in series. It is evident that by converting the discriminatingfactors to scalar values, and combining them serially, the summationwill produce a single discriminating function which can be manifested ina single measuring circuit, indicated at 62, the circuit beingrepresented as terminating in terminals 64 and 65. Since thediscriminating factors across each output of the rectifiers, arederived, respectively, from the individual sequence-components 11, I2and I0, the registration response, or discriminating function, in themeasuring circuit 62 will be the sum of the individual scalar quantitiesderived from these components and is represented by Equation 1.

By varying the value of the resistance R0, and each or both of thevalues of the resistances 2E! and 34 (in which case the impedances Z andY should also be proportionately varied, if necessary), it is possibleto control the magnitudes of the constants in, kg and k0. Or by treblingthe magnitude of resistance 34, and correspondingly trebling the mutualimpedance of the windings in impedance Y, this impedance will physicallyduplicate the impedance Z. However, in actual practice of my invention,I01 and It; may be equal, and he can be readily varied by varying thevalues of the resistance R0. representative relationships of the networkshown in Fig. 1 will yield a discriminating function in the measuringcircuit which may be represented by this equation obviously being theequivalent of Equation (1) under the assumed conditions.

However, for a practical embodiment of the relaying equipment inaccordance with my invention, it is desirable to provide taps or othercommon adjustment features by which the weighting constants of eachsection of the network can be controlled so that the equipment can be ofgeneral application, being adjustable to obtain the relative weightingsbest suited for the particular alternating-current line or device towhich it is applied. Any one, or a combination, of the weightingconstants will, in general, be determined by the characteristics of theapparatus In this case the being protected so as to render the equipmentbest suitable to the particular loads of the protected apparatus, thefrequency of expectable fault types, the discriminating difficulties,the force coordination of the responsive devices, or other factors thatare usually involved and considered.

The measuring circuit 62 can be utilized with any suitable apparatus.For example, the terminals 64 and 66 might be connected to a suitablerelay for operating, in response to a predetermined value of thediscriminating function, a tripping coil of a circuit breaker. In such acase, the system of Fig. 1 becomes an overcurrent protective device. Orthe terminals 64 and 56 may be connected to suitable apparatus of apilot wire system, a similar system being provided at the other end ofthe protected section, and in Fig. 2 I show a modified form of myinvention in such a pilot wire protective system wherein the discriminating function is represented by In Fig. 2 the protected linesection, represented by A, has end terminals provided with protectiveequipment B and C, respectively, the protective equipment being joinedby pilot wires 68 and 10. In the system shown in Fig, 2, the brokenlines are inserted as indicative of extended lengths of wires.

Each of the terminal end protective equipment comprises a network forderivingonly scalar quantities representative of the positive-sequencecurrent-component and the zero-sequence current-component. This is doneby providing each of the current protective equipments with an impedanceZ and a resistance 20 connected as shown in Fig. 1 to yield adiscriminating factor across the terminals 24 and 26 which isrepresentative only of the positive sequence component, and a resistanceR'o in the neutral connection of the current transformers which willyield a discriminating factor across the terminals 52 and 54',representative solely of the zero-sequence component, in accordance withthe principles outlined in Fig. 1.

The circulating-current protective system shown in Fig. 2 is one similarin its general aspects to that shown in Fig. 11 of my aforesaid patent,and comprises operating coils 12 across the respective measuring circuitterminals 64' and 66, and restraining coils 14 in series in themeasuring circuit, a pair of coils T2 and 14 at each terminal operatingupon a polarizing relay 16 which, in turn, controls a tripping coil 18of a circuit breaker 80.

Since the discriminating functions at each of the terminals B and C ofthe protected section are unidirectional, insulating transformers cannotbe used to isolate the terminal equipment from the pilot wires toprotect this equipment from voltages-to-ground due to induced voltagesin the pilot wires. However, by using several neutralizing transformers82 at the ends of the pilot wires, and grounding capacitors 84 from eachterminal end of each pilot wire to ground, as described in my aforesaidapplication, the induced voltages can be neutralized and renderedharmless.

Fig. 3 represents a system similar to Fig. 1, but which can be utilizedfor overcurrent protection of an electric device whose neutral is eitherungrounded or not very well grounded so that the proportion of thediscriminating factors due to the zero-sequence component flowingthrough the diiferent sections P and N will not appreciably affect theactual discriminating factors,and the totalized scalar discriminatingfunction obtained from the series-connected pairs of terminals 24-26",36"38", and 52"'54" does not objectionably depart from its value asrepresented by Equation 1.

The system of Fig. 3 is also useful for protection Where high relativezero-sequence weighting is desirable in systems which might, at times,have fault currents with relatively small zero-sequence components,making desirable an accentuated zero-sequence discriminating factor totake care of conditions of this kind.

In Fig. 3, it may be observed that the line currents Ia, Ib and I0 flowto the neutral point 86 which is connected by wires88 and 90 to theneutral of the current transformers, a resistance 92 being inserted inseries with these conductors for deriving a quantity representative ofthe zerosequence current-component. In order'to magnify the effect ofthis zero-sequence component the resistance 92 is made high sothat thevalue of k0 is high, and will, therefore, make the discriminating factorhalo of a magnitude approaching or even exceeding the magnitude of thediscriminating factors resulting from the positiveand negative-sequencecomponents, although the actual value of the zero-sequence componentitself might be considerably less than the expectable value of the othersequence components. In this modification the outputs of the rectifiersare also serially connected and operate a relay '94 controlling thetripping circuit of a circuit breaker 96, when the discriminatingfunction indicates an excess current in the main lines. I

In the system of Fig. 1, the discriminating factors due to the differentsequence-components are actually representative of these componentswhereas in Fig. 3, the discriminating factors across the pairs ofterminals -24-25" and 36"38 are modified somewhat by the zerosequencecomponent flowing through the connected sections of the network, but theextent of the modifying is negligible in ungrounded systems or poorlygrounded systems, or in systems where high relative zero-sequenceweighting is to be used, for which this embodiment is useful.

As an example of the application of the fundamental Equation 1, bymaking k1 and its the same and k0 five times either of these, themagnitudes of discriminating functions resulting from the 10 differenttypes of expectable faults on a fairly well grounded three-phase line,will fall within a small range, and may be made to fall within 1 a rangeof less than two to one between minimum and maximum magnitudes, evenwith maximum phase-angle displacements between the sequencecurrent-components themselves. Consequently, a particular advantage ofmy system resides in this fact that the phase-angle between thesequence-components is not a factor in the discriminating functionpresent in the measuring circuit since each component is first rectifiedso that only scalar values are added or combined. By the introduction ofa factor due to the negative-sequence component, the percentage ratio Wof the lowest fault-response as compared to the highest fault-responsefor any of the types of faults which might occur on a given line, can

be made to approximate unity and kept even above 50 per cent for allconditions. The values of the different constants 100, kr and 162 willdepend on thecharacteristics of the protected de-' vice and by suitableadjustments in the phasesequence networksections, the constants may bevaried to give the desired'percentage ratio W.

In some systems where the scalar addition of the discriminating factorsdue to the positivesequence current component and the zero-sequencecurrent component is sufficient for protective purposes, the possibilityof an excessively low discriminating function which might, for example,occur when the zero-sequence currentcomponent has very large phasedisplacement as compared to the positive-sequence currentcomponent, iseliminated.

In order to reduce the internal impedance of the. different networksections from which the different discriminating factors are obtained,it may be desirable to have the primary windings of the impedances Z andY of relatively large number of turns as compared to the secondarywindings'and for the networksection of the negative-sequence componentthe secondary winding 48 may be a small number of turns as compared tothose of the primarywindings 42 and 44, the value of the resistance 3being correspondingly made smaller or a transformer interposed thereatfor the purpose. If desired, in some embodiments smoothing filtersincluding capacitors may also be connected across the output ends ofsome or all the'rectifiers where slower relaying is involved, suchcapacitors further reducing the effects of phase-angle displacementbetween the different current-components.

Additionally, voltage limiters, such as shown in M. A, Bostwick PatentNo. 2,183,537, issued December 19, 1939, and assigned to theWestinghouse Electric & Manufacturing Company, may be utilized,preferably across thealternating-current input terminals of therectifiers, and so designed as to limit its voltage output only afterthe responsive relay setting has been exceeded by an adequate margin tosecure the desired speed.

In the above description, it is understood that, in general, allalternating current-electric quantities in the networks are vectors.

The systems just described mave many features and advantages describedin myaforesaid patent, and while I have illustrated my invention in anumber of different forms, I desire it to be understood that suchillustrations are not by way of limitations since it is obvious to thoseskilled in the art that many modifications of the precise details andnetworks may be adopted or equivalent substituted without departing fromthe teachings of my invention. Another embodiment of my invention, moreespecially for impedance relaying, is'shown in my Patent No. "2,242,951of May 20, 1941, for which'a reissue patent application has been filed.

I claim as my invention:

1. A three-phase device having a three-phase line, a single set ofcurrent transformers for said line, networks connected to saidtransformers comprising a plurality of means including impedance devicesand circuits having three distinct pairs of connections for obtaining,respectively, across said pairs of connections, unidirectional voltagesindividually representative of the positive-sequence, negative-sequence,and zerosequence components of the line-currents, and means foralgebraically adding the said obtained voltages for deriving a responseto line-conditions, which response is a function of variables dependentsolely on said obtained'voltages.

2. A three-phase device having a three-phase line, current transformersfor said line, networks connected to said transformers comprising aplurality of means including impedance devices and circuits having threepairs of connections for obtaining, respectively, across each of saidpairs of connections, a sequence-voltage representative of thepositive-sequence, negative-sequence, and zero-sequence components ofthe line-currents, and utilization means including rectifiers forrectifying and serially combining said sequencevoltages.

3. Means for utilizing a single relay to respond to any one of aplurality of different kinds of faults in a three-phase electricaldevice to be protected, comprising the combination, with said relay, ofselective phase-sequence filter means and circuit means to said relayfor energizing said relay with a current corresponding, in apredetermined manner or manners, to the values of a combination ofrectified, weighted sequence-components derived from the phase-currentsin the protected device, said filter means including means for applyingto said circuit means, in series, individual rectified voltagesrepresentative of the zeroand positive-sequence components of thephase-currents in said protected device.

4. Means for utilizing a single relay to respond to any one of aplurality of different kinds of faults in a three-phase electricaldevice to be protected, comprising the combination, with said relay, ofselective phase-sequence filter means and circuit means to said relayfor energizing said relay with a current corresponding, in apredetermined manner or manners, to the scalar values of a combinationof rectified, weighted sequencecomponents derived from thephase-currents in the protected device, said filter means includingmeans for applying to said circuit means, in series, individualrectified voltages representative of the zero-, negative-, andpositive-sequence components of the phase-currents in said protecteddevice, with the magnitude of said series combination of rectifiedvoltages within a relatively narrow predetermined range for thedifferent kinds of faults.

5. An electrical system responsive to the linecurrents in a three-phasedevice, comprising a plurality of network means for obtaining electricalquantities 76010, 10111, and R212, where I0, I1, and I2 are the zero-,positive-, and negativesequence components of the line-currents, and k0,k1, and R2 are selected constants, and means including a utilizationcircuit, for rectifying said quantities to obtain scalar values of each,and algebraically adding, in a predetermined manner or manners, only thesaid scalar values to derive a resulting single unidirectionalelectrical quantity utilizable as a discriminating function in saidutilization circuit.

6. A three-phase device having a three-phase line, network means forderiving individual singlephase electrical quantities representative,respectively, of a rotationaland a zero-sequence-component of theline-currents, said network means having a plurality of pairs ofjunctions, one for each of said sequence-components, rectifier meansconnected to said junctions to convert said individual single-phaseelectrical quantities to individual unidirectional electricalquantities, and a utilization circuit including the outputs of saidrectifier means in series whereby said unidirectional quantities arealgebraically added.

'7. A three-phase device having a three-phase line, network means forderiving an individual electrical quantity 1010, an individualelectrical quantity R111, and an individual electrical quantity 10212,where I0, I1 and I2 are representative of the zero-, positive-, andnegative-sequence components of the line-currents, and I00, I01 and k2are weighting constants, means for converting said quantities to scalarquantities, said means including a utilization circuit in which saidscalar quantities are algebraically added to provide a single electricalquantity in said circuit represented by lkolol-l-lkihl-l-lkzlzl, thebars being indicative of scalar values, and fault-responsive meansresponding to the last said quantity.

8. A three-phase device having a three-phase line, network means forderiving an individual electrical quantity i610 and an individual electrical quantity kiIi, where I0, and I1 are representative of the zero-,and positivesequence components of the line-currents, and kc, and k1 areweighting constants, means for individually converting said quantitiesto scalar quantities, said means including a utilization circuit inwhich said scalar quantities are algebraically added to provide a singleelectrical quantity in said circuit represented by ]koIo[+|k1I1|, thebars being indicative of scalar values, and fault-responsive meansresponding to the last said quantity.

9. A difierential-protective apparatus for an alternating-currentelectrical device having lines including a plurality of separatedterminals where current may enter or may leave, comprising means at eachof said terminals for deriving quantities including a plurality ofunidirectional quantities, each of which is individually representative,in some manner or manners, of selected sequence-components of theline-currents at the corresponding terminal, said means including meansfor combining said derived quantities in a predetermined manner ormanners, and comparing means including connections between saidterminals, having the property of comparing the combined electricalquantities at each of said terminals for the detection of faultyconditions in said electrical device, the last said means includingdevices operable by said comparing means.

10. An electrical system responsive to the electrical quantities in amulti-phase device, comprising a plurality of means for obtaining electrical quantities MO, MP, and hill, where O, P, and N are the zero-,positive-, and negativesequence components of the said electricalquantities, and 760,161, R2 are selected constants, and means includinga utilization circuit, for rectifying said quantities to obtain scalarvalues of each, and algebraically addltively combining all of saidscalar values in a predetermined manner or manners to obtain a singleunidirectional electrical quantity utilizable as a discriminatingfunction in said utilization circuit.

11. A three-phase device having a three-phase line, means for derivingindividual single-phase electrical quantities representative,respectively, of a rotationaland a zerosequence-component of theelectrical quantities, said means having a plurality of pairs ofjunctions, one for each of said sequence-components, rectifier meansconnected to said junctions to convert said individual single-phaseelectrical quantities to individual unidirectional electricalquantities, and a utilization circuit including the outputs of saidrectifier means in series whereby said unidirectional quantities arealgebraically added.

12. A three-phase device having a three-phase line, means for derivingan individual electrical quantity 1000, an individual electricalquantity kiP, and an individual electrical quantity kzN,

where 0, P, and .N are representativelof thedzeropositive-, andnegative-sequence components of theielectrical.quantities:ko, ki and R2are weight.- ing'constants, means (for converting .said quantities tovscalar .quantities, said means including a utilization circuit in whichsaid scalar quantities are algebraically added to provide .a singleelectrical quantity in said circuit represented by }koOl+lk1P]+l-Ic2N|,the bars being indicative cf scalar values, and fault-"responsive meansre-. spending to .theilastisaid quantity.

13. A three-phase device having a :three-phase line, means for derivingan individual electrical quantity k0 and an individual electricallquantity klP, where 10, and vP :are representative of the zero-, andpositive-sequence components of the electrical quantities, and Jan, andJcrare weighting constants, means for individuallyconverting saidquantities to scalar quantities, said means including a utilizationcircuit in which said .scalar quantities ,are algebraically added toprovide a single electrical quantity in .said circuit represented :bylko'OleHlciRl, thebars .heing indicative of $502.12.! values, and;fault-=responsive means respending to :the :last said iguantity.

14., The combination, with a .zpqlyphase ielectricalapparatus, ,of aplurality of :difierentmeans for producing :a plurality of difierentsinglephase relaying quantities l-responsive .to. differentphase-sequence components .of a predetermined electrical quantity -.ofsaid 'po'lyphase electrical apparatus, at least one of saidsingle-phasevrelaying .quantities being selectivelyresponsivesu'bstantially exclusively tp a rotational phase-:sequencequantity, .and v at least one other ;of ;said single-phase relaying.quantities being responsive to a .zero phase-{sequence quantity,separate means :for individually rectifying .the .several singlen-phaserelaying quantities, and means for combining, only :in series-circuitrelation, said single-phase relaying .quantities :for obtaining a jointresponse dependent .upon the .rectifiedquantities.

EDWIN "L. HARDER.

